1. Field of the Invention
The invention relates generally to the manufacture of fuel cells, and more particularly to the testing of fuel cells.
2. Related Art
Fuel cells are used as sources of energy in a wide variety of applications in diverse industries ranging from telecommunications and health services to transportation and defense. An important type of fuel cell, which uses a solid oxide or ceramic electrolyte, is known as a solid oxide fuel cell (SOFC). A typical solid oxide fuel cell is a few millimeters thick and does not provide adequate power for most applications. Typically, multiple SOFCs are connected together to increase the output voltage and/or current, with the resultant set of connected SOFCs termed an SOFC “stack.”
Despite the known importance of fuel cell stacks, the cost of manufacturing them remains high, and it would be advantageous to reduce this cost to fully realize the potential that fuel cells have to offer. During the manufacture of fuel cells stacks, each stack is tested to ensure that all the fuel cells in it are working properly. The cost of the testing process, however, is a major contributing factor to the overall manufacturing cost. Accordingly, one way to reduce manufacturing cost is to reduce the cost of testing fuel cell stacks.
One way to test whether a fuel cell is functioning properly is to measure the voltage it outputs. The fuel cell may be activated and provided with fuel; the resultant voltage output may be measured and analyzed. Deviations in the measured voltage from the voltage that the fuel cell is expected to output may indicate that the fuel cell is defective.
At room temperature, the ceramic electrolytes used in SOFCs behave as insulators, and they do not become electrically active until they reach much higher temperatures. As a result, SOFCs and SOFC stacks operate at very high temperatures, typically over 500 degrees Celsius, which considerably complicates testing SOFCs because the testing process must also be performed at these high temperatures.
In the art, it is known to test a fuel cell stack by welding high-temperature wires to each fuel cell. The SOFC stack is placed in a furnace, with the high-temperature wires connected to a high-precision voltmeter outside the furnace. The voltage potential on each individual fuel cell may then be measured and analyzed to detect defects.
If the analysis of measured voltage potentials reveals that a fuel cell in a fuel cell stack is not operating fully as desired, the manufacturing process of the fuel cell stack may be altered. For example, following testing, functioning fuel cell stacks may be packaged for shipping, whereas stacks with faulty fuel cells may be discarded or reworked to replace the faulty cells.
This conventional SOFC testing process is expensive. The equipment, such as high-temperature wires, the time and labor required to weld these wires to individual fuel cells and to unweld these wires from the fuel cells all contribute to the high cost. Moreover, unwelding the high-temperature wires after testing may damage the fuel cells. This conventional approach is not amenable to high-throughput manufacturing.